It's OK as long as you don't feed him on it (he might ingest some). Pine and cedar are toxic, some organic bedding like coconut and corn cob can mould faster so keep on top of that, Carefresh is used by some without problem but it can dry your snake out if you live in an arid area, I've heard some repti-bark has mites (some people like to freeze the bags for a while before use). Sand us usually frowned upon, aspen is the most popular bedding here, other use newspaper and astroturf.
This is what I've gathered from reading the many threads on the subject that pop up around here. I would advise looking into anything I've written to get more information, I'm not an expert.
I use aspen and love it.